In dry layers, water layers, gas layers, abnormally high-pressure layers and other special layers that appear during the execution of a formation testing in middle-shallow layers, to block an abandoned layer, such a bridge plug is usually used to seal the layer, and a permanent bridge plug is used to seal a formation-tested well for which no short-term development plan is made. Besides, the bridge plug is also used to block a tested layer of a deep-seated gas well to ensure the successful implementation of a technical process such as a shallower pool test and a fracturing reformation.
Currently, there are two main types of dissolvable wellbore plugs: dissolvable bridge plugs and dissolvable ball seats, both of which have their defects, specifically,
1: defects of dissolvable bridge plugs:
1) their sealing part is a rubber cylinder, which is difficult to be completely dissolved because of its large volume and high dissolution condition and therefore blocks a wellbore frequently in the later stage of construction and affects the oil output of an oil well;
2) their metal part has a large volume and produces many dissolved matters, blocking a wellbore easily; and
3) complicated in structure and high in production cost.
2: defects of dissolvable ball seats:
1) their construction procedures are tedious because the pre-arrangement of a working barrel is necessary;
2) the use of a specific placing tool is inevitable; and
3) high in machining precision and thus high in production cost.